Noble metal alloys are widely employed in dentistry and other applications where inertness to the environment is essential or where other characteristics provided thereby are desirable. In the production of dental restorations, gold and platinum alloys have been preferred because they exhibit desirable properties during casting and hardening, and various porcelains have been developed for use therewith to provide the desired wear properties and aesthetic appearance.
As a result, it has been generally essential to use noble metal alloys which exhibit a high solidus temperature so as to resist deformation during the firing of the porcelain coating thereon and which will also exhibit a high hardness sufficient to resist impacts upon the face and pressures occurring during mastication of foods and the like.
Unfortunately, many of the gold alloys which are available either exhibit low melting points which create problems during the firing of the porcelain coating, or excessively high costs. Moreover, some gold alloys exhibit excessive yellow coloration so as to require special opaque porcelain compositions to mask the yellowness of the casting. In order to effect optimum bonding of the porcelain coating to the noble metal alloy casting, it is generally desirable that the casting have an oxide coating which will permit the porcelain coating to bond thereto through diffusion.
Palladium has been proposed and utilized in a number of alloys with gold to increase the solidus temperature but frequently excessively lowers the thermal expansion of the alloy so that it is no longer compatible with many dental porcelains. Moreover, substantial problems are frequently encountered with gold/palladium alloys from the standpoint of achieving the necessary hardness for dental applications and from the standpoint of obtaining a casting to which the porcelain coating may be readily bonded. This is particularly true with porcelains which are based upon feldspar and nepheline syenite.
It is an object of the present invention to provide a novel noble metal alloy for dental and other applications which is substantially inert and which exhibits both high hardness and a relatively high solidus temperature.
Another object is to provide such an alloy exhibiting a thermal expansion coefficient approximating that of a wide range of porcelain materials so that it will form a desirable substrate therefor in the manufacture of dental restorations.
Still another object is to provide such an alloy wherein a porcelain coating may be bonded thereto by diffusion to provide a rugged dental restoration.
A further object is to provide rugged and attractive dental restoration utilizing an inert, hard noble metal alloy and a porcelain coating which is firmly bonded thereto.